Detection of marihuana use through analysis of biological samples, such as urine or blood, is coming into more widespread use. Because use of urine samples involves a non-invasive and more convenient process, detection of metabolites of .DELTA.-9-tetrahydrocannabinol in urine has begun to find greater popularity. Additionally, the use of such assay procedure has begun to develop greater importance and more widespread use not only because of its use to initially detect marihuana users but as an adjunct of drug counseling programs as a screening procedure to monitor compliance with withdrawal procedures and continued abstinence from marihuana use.
Of the several metabolites of .DELTA.-9-tetrahydrocannabinol found in urine the major is 11-nor-.DELTA.-9-tetrahydrocannabinol-9-carboxylic acid, hereinafter referred to as THC-COOH, in either its free or conjugated (glucuronide) form. Various non-automated processes exist for detection of THC-COOH in urine, such as thin layer chromatography, gas chromatography, gas chromatography/mass spectrometry, radioimmunoassay, enzyme multiplied immunoassay and more recently high performance liquid chromatography (HPLC). However, such processes are quite labor intensive and due to the numerous and varied interferents in the urine sample are quite cumbersome to carry out. Additionally, it is difficult to measure THC-COOH in urine because of the complex nature of this matrix. The extraction of THC-COOH from urine is rendered more difficult because THC-COOH is one organic acid among a large number and variety of organic acids present in urine. A number of these organic acids have chromatographic properties which are similar to THC-COOH and will interfere with its measurement. Therefore, in order to be able to obtain a meaningful and relatively quick measurement of THC-COOH in urine one must be able to selectively extract it from the urine sample.
Current techniques for screening total urine samples for the presence of THC-COOH are generally either by thin layer chromatography or the Enzyme Multiplied Immunoassay Technique (EMIT) of Syva Company. Once a positive sample is detected a confirmational analysis is performed, usually by gas chromatography/mass spectrometry. However, with adequate cleanup of the urine sample, that is concentration of THC-COOH in the urine sample, and the use of an internal standard, confirmation by HPLC is possible. Thus, a great need exists for a much more satisfactory method of cleanup of urine samples to concentrate THC-COOH present in said samples. A bonded phase chromatographic packing that uniquely and specifically extracts THC-COOH from human urine would be highly desirable. Moreover, a bonded phase that is specific enough for THC-COOH yet permits selective elution of THC-COOH from the column without removing the impurities from the column or selective elution of the impurities from the column without removing the THC-COOH would be most desirable. A bonded phase that provides a purified urine extract clean enough to permit a more sensitive analysis of THC-COOH by confirmational methods, such as by HPLC, is greatly needed. Impure extracts also result in high and noisy baselines that decrease the capability for detecting low levels of THC-COOH. Cleanup of urine samples sufficient to detect low levels of THC-COOH would be most desirable.